When to replace a car battery?

Updated: July 16, 2022
The 12-volt battery in your car stores the electric power to start your engine. When the engine is started, the alternator generates the electric power and recharges the battery.
Car Battery Car battery.

A new battery has a full capacity or ability to hold charge. It can store enough electric charge to turn over your engine multiple times and power the electrical systems when the car is parked. Over time, however, the battery loses its capacity and becomes weak.

One day, a weak battery will not be able to start your car. Often, this happens on a cold morning. When to replace the battery? The battery need to be replaced before its capacity drops to a critical level.

How long do car batteries last?

On average, a car battery lasts from 5 to 7 years. The battery lasts longer if the vehicle is driven daily and the battery is kept fully charged. When the vehicle is parked for extended periods of time, the battery deteriorates sooner. The size of the battery matters too: larger batteries last longer. We have seen larger batteries lasting up to 10 years.

How can you tell that the battery capacity is getting low?

When the battery's capacity becomes low, you might notice that at times, the engine turns over slower, not as eagerly as before. The dash lights may flicker when starting the vehicle. Another sign is when you operate your power windows after the engine is turned off, the windows move much slower than when the engine is running. Your vehicle might also need frequent boosting.

Sometimes you also may notice that the lights turn dimmer when the engine is idling, but become brighter again when the engine is revved. The excessive corrosion at the battery terminals and cables (see the photo) also suggests that the battery is getting weaker.

Can the battery capacity be tested?

Car Battery Tester Testing the battery capacity with a battery tester.
Yes, the battery capacity is often measured in CCA or Cold Cranking Amps. A new average-size battery like the one in the top photo is typically rated between 520 and 650 CCA.

Many automotive repair shops can test your battery with a battery tester (in the photo). The battery tester can measure the actual CCA and compare it to the new battery CCA rating. The battery CCA rating is marked on the battery itself, see the photo.

The battery tester can also test the alternator and the charging system. Read more about the charging system: When does the alternator need to be replaced?
Testing a car battery with Battery TesterBattery and charging system test printout

The battery and charging system test, known as the AVR test, costs from $20 to $50. Some auto parts stores such as Autozone or O'Reilly Auto Parts offer a battery test at no charge. Many car dealers and repair shops often offer a free battery test as a part of a larger service or a seasonal promotion.

After the test, you might get a printout showing the battery CCA rating and the measured CCA. The printout will indicate if the battery should be replaced or if it's in good condition. The printout may also indicate that the battery needs to be recharged first and then re-tested. See the sample printout in the photo.

Can you test a battery with a voltmeter?

Battery voltage test Testing the battery state of charge with a voltmeter.
The battery voltage is an indicator of the state of charge of the battery. A fully charged battery should read 12.6 volts or more with the engine off. However, even an old failing battery with low capacity will show 12.6 volts when fully charged.

To test the capacity of the battery, the battery voltage needs to be tested under load. The longer the battery can hold the voltage under load, the larger its capacity.

For example, if the fully-charged battery voltage with the engine OFF and headlights ON drops from 12.6 volts to less than 11.5 volts in a couple of minutes, the battery's capacity is low. If the battery voltage with engine OFF and headlights ON stays close to 12 volts even after 10 minutes, the battery is good.

Can a problem with battery terminals cause the vehicle not to start?

Corroded vs Serviced Battery Terminal Corroded vs. serviced battery terminal.
Yes. If one of the battery terminals is loose or corroded, it may cause many problems including a no-start, Check Engine light, stalling, as well as lack of the electric power steering assist. Many dealers and reputable repair shops visually inspect the battery terminals during regular oil changes.

Your mechanic may recommend servicing battery terminals if they are corroded as in the photo. The battery terminal service costs from $25 to $50. It includes cleaning the battery posts and terminals and applying a protective spray or grease.

How much does the battery replacement cost?

A new car battery costs from $140 to $550 and your dealer may charge another $30-$50 to have it replaced. Replacing a car battery as a do-it-yourself project is not very difficult, but the battery is heavy (30-45 lb). Lifting it out of the car can be hard on your back. An old battery is often covered in electrolyte, which is very acidic and can burn your clothes or skin. Here is a video from O'Reilly Auto Parts.

Our recommendation is to leave it to the pros. Some cars require a specific battery type. To make sure, check the vehicle owner's manual or consult with your local dealer.

In some cars, the battery management system needs to be reset when changing the battery

Battery current sensor Battery current sensor.
Some modern cars are equipped with a battery management system that is designed to improve the fuel economy and battery life. It works by monitoring the battery current, state of charge and state of health. When the battery is replaced, the battery management system may need to be reset, so it knows that the battery is new.

In some cars, you can tell that the vehicle is equipped with a battery management system if it has a battery current sensor on one of the terminals, like the one in the photo. If the battery management system is not reset, it might think that the battery is old and weak and some of the electric features will not work correctly.

What is an AGM or Absorbed Glass Mat battery?

AGM Battery AGM Battery.
An AGM battery is a modification of a traditional lead acid battery. In a traditional lead acid battery, cells are filled with liquid electrolyte. In an AGM battery, the fiber glass mats soaked in electrolyte are sandwiched between the lead plates. So the main difference is that in an AGM battery the electrolyte is not free-flowing but rather contained in the absorbed glass mats like in a soaked sponge. AGM batteries are supposed to be more durable, resistant to vibration and hold the charge longer when not in use, however they are also more expensive and more sensitive to overcharging.

Are AGM batteries really worth it?

If your car has a Start-Stop system it might require an AGM battery. Many motorcycle, ATV and RV owners prefer AGM batteries for their performance and durability. However, if your car doesn't require an AGM battery, a traditional acid battery of the right type is more suitable. AGM batteries don't like overcharging and if the vehicle is not designed for an AGM battery, this could be a problem on a long trip, especially in hot weather. Check your owner's manual for the correct battery type.

Where to recycle an old car battery?

Some automotive repair shops and car dealers will accept your old battery for recycling. For example, you can find the nearest place to recycle your old battery at the Interstate Batteries website.

How long is the battery warranty?

In most cars, the battery is covered under the basic bumper-to-bumper warranty. In some cars, the battery coverage is pro-rated. This means, for example, the labor might be fully covered, while the part might be covered 100 percent within the first year, 50 percent within the second year and so on. You can find the warranty coverage details in your Warranty Guide brochure, or on the manufacturer's website.

How to boost a car when the battery is low on charge?

To boost a car, you will need a portable booster or jumper cables to boost from another car. Your owner's manual has the proper instructions. Be careful, if the booster cables are connected to wrong terminals, it may cause a big spark and some fuses and other electrical components could be fried.

How long does it take to recharge a good battery that is low on charge?

If the battery is still good, 20-40 minutes of running the engine or driving is usually enough to recharge it.
However, be aware that in some cars with electric power steering, the steering assist might not work properly until the battery is sufficiently charged. This can make driving with a low battery dangerous.
If a good battery has not been used for an extended period of time and is completely drained, it might need longer time to recharge.

In some high-mileage cars, the engine may run rough at idle or even stall after replacing the battery. This happens because when the battery is disconnected, all learned settings in the engine computer, including the idle speed, are reset. For this reason, some older cars may require the idle speed re-learn after the battery is replaced. The procedure varies for different cars, but it won't take you long to google it. To avoid this problem, many repair shops use a simple memory saving device that keeps the engine computer powered during battery replacement. In modern cars, the idle speed is re-learned as you drive.